Applying conformal mapping method to Hybrid Nodal Green's Function Method for two-dimensional simplified HTTR core calculation

A new feature for the core calculation of prismatic-block type of Very High Temperature Reactor (VHTR) was added to our in-house code NuCoT. The nodal method used was Hybrid Nodal Green's Function Method (HNGFM). The conformal mapping method was adopted for handling the hexagonal geometry. The accuracy of the new capability was verified through several benchmark problems. Results of comparable accuracy with other developments were obtained. The method was further verified by performing a 2D simplified HTTR problem and compared with MCNP result. The statistical errors of k(eff) was <10 pcm and of fission power was <0.1%. The results of Hex-capability of NuCoT showed that using supercell method for cross section generation for homogenization of fuel block gave more accurate results than using single fuel block with periodic boundary condition. For the control rod block that contains three large void channels, using anisotropic diffusion coefficient resulted in more accurate k(eff). In the all-rods-out condition and the partially-controlled condition, the difference in k(eff) was <140 pcm and in maximum power was <0.8%. In the all-rods-in condition, the error in k(eff) and maximum power error were 413 pcm and 1.1%, respectively. (C) 2018 Elsevier Ltd. All rights reserved.